There are various starting materials that are further processed in a cracking furnace for the operation of an ethylene furnace, which is also referred to as cracking furnace. Among others, such starting materials are, naphtha, also referred to as liquid starting material (liquid feed), or gas, also referred to as gaseous starting material (gas feed) with a high ethylene content. Both starting materials are heated to a high temperature in a cracking furnace and subsequently cooled immediately with a quenching system, which is also designated by QS for short.
A quenching system or QS with a special configuration is needed depending on the starting material because the physical properties of the starting materials are different. Gas as a starting material may be cooled further downwards, for example, from 900° C. to 150° C., than a liquid starting material, which is cooled from about 900° C. to 350° C., because the condensation of gas starts only at markedly lower temperatures.
Consequently, a quenching system for gas feed mode more often than not consists of a primary heat exchanger or referred to as PQE for short and/or a secondary heat exchanger or referred to as SQE for short and a tertiary heat exchanger or also referred to as TQE for short.
A quenching system for liquid feed mode consists only of a PQE and a SQE which are connected in series. A TQE, which is always used as a feed water preheater or boiler feed water preheater, is not installed in such an arrangement, wherein the PQE and SQE are each connected as evaporators and are also operated as such.
DE 10 2014 018 261 A1 is mentioned as state of the art.
In order to be able to operate a quenching system both with liquid as well as with gaseous starting material, a PQE and an SQE and a TQE must be installed. The TQE on the gas side shall be bypassed by means of a bypass in case of a liquid feed mode of operation.
The current mode of operation of a quenching system for gas feed and for liquid feed according to the state of the art is carried out with such a bypass circuit. A gas inlet valve provided in front of a gas inlet pipe of a TQE is open and a bypass valve arranged in the bypass of the TQE is closed in case of a gas feed operation. The gas inlet valve is closed and the bypass valve is open in case of a liquid feed operation.
The drawbacks of the used arrangement of a quenching system for a gas feed and liquid feed mode of operation according to the state of the art are that such an arrangement with bypass control needs a very large space and hence causes high costs, aside from the fact that the technical arrangement and mode of operation cannot sufficiently meet the requirements set for such a quenching system in terms of reliability, ease of performing repairs and ease of maintenance.